Method and control unit for operating an automatic transmission of a motor vehicle

Abstract

Method for operating an automatic transmission (3) of a motor vehicle, wherein, when the cruise control function is active and the actual speed of the motor vehicle is less than the target speed of the motor vehicle, load is requested from a drive unit (1) of the motor vehicle to reduce the difference between the target speed and the actual speed, and depending on at least one shift map, at least one downshift and subsequently, if necessary, at least one upshift is requested from the automatic transmission (3), characterized in that Depending on the actual speed and the difference between the target speed and the actual speed, a target acceleration for the motor vehicle is determined. For gears that are available for downshifting, a gear-dependent maximum acceleration is determined, Depending on a comparison between the target acceleration and the gear-dependent maximum accelerations, a limiting gear is determined. Then, if the target gear of a downshift determined depending on the switching characteristic map or maps is smaller than the limiting gear, a downshift is limited to the limiting gear, whereas if the target gear of a downshift determined depending on the switching characteristic map or maps is larger than or equal to the limiting gear, a downshift to the target gear determined depending on the switching characteristic map or maps is permitted.

Description

[0001] The invention relates to a method and a control device for operating an automatic transmission of a motor vehicle.

[0002] Automatic transmissions in motor vehicles are connected between a drive unit and an output drive. An automatic transmission performs gear shifts automatically, converting engine speed and torque depending on the selected gear, thus transferring the power of the drive unit to the output drive.

[0003] Automatic transmissions with multiple shift elements are known in practice, wherein in each non-positive gear of the automatic transmission a first defined number of shift elements are closed or engaged and a second defined number of shift elements are open or disengaged. Automatic transmissions are known which comprise at least one positive shift element and at least one frictional shift element. A positive shift element can be designed as a claw. A frictional shift element can be designed as a clutch or brake. When executing a gear change from a non-positive actual gear to a non-positive target gear, at least one shift element of the automatic transmission is opened or disengaged and at least one other shift element of the automatic transmission is closed or engaged.

[0004] It is known from the prior art that a motor vehicle with an automatic transmission can utilize a cruise control function. A cruise control function is also referred to as cruise control. A cruise control function regulates the speed of the motor vehicle such that the actual speed of the motor vehicle corresponds to a desired target speed. When using an adaptive cruise control function, known as ACC (Adaptive Cruise Control), the motor vehicle can be automatically decelerated to a speed below the desired target speed, namely when the distance to a preceding object falls below a certain threshold.

[0005] DE 100 21 770 A1 discloses a method for controlling an automatic transmission for a motor vehicle with a cruise control function. This prior art discloses that, when the distance to a vehicle ahead falls below the target speed during an adaptive cruise control function, the vehicle is decelerated to a speed below the target speed. Once a sufficient distance has been restored between the object ahead and the motor vehicle, the motor vehicle then automatically accelerates back to the target speed. DE 100 21 770 A1 further proposes selecting a driving program depending on external influences on the motor vehicle, in particular depending on the road gradient.

[0006] DE 197 16 088 A1 discloses a vehicle control system for a motor vehicle with an automatic transmission and a cruise control function. The vehicle control system disclosed therein has an obstacle detection device for detecting obstacles that impede the movement of the motor vehicle. When an obstacle is detected, the control of the automatic transmission is influenced.

[0007] If, with the cruise control function active, the actual speed of the vehicle is lower than the target speed, and the difference between the target speed and the actual speed needs to be reduced, load is requested from a drive unit of the vehicle and, depending on at least one shift map, at least one downshift and, if necessary, then at least one upshift of the automatic transmission is requested. Under certain circumstances, several downshifts may be requested in succession, which in high-performance vehicles with high-performance drive units can lead to high accelerations that are perceived as uncomfortable. This is a disadvantage.

[0008] From DE 10 2005 031 764 A1 a vehicle control system for a motor vehicle with an automatic transmission and a cruise control function is known.

[0009] Based on this, the invention is based on the object of creating a novel method and a control device for operating an automatic transmission of a motor vehicle.

[0010] This object is achieved by a method according to patent claim 1.

[0011] According to the invention, a target acceleration for the motor vehicle is determined depending on the actual speed and the difference between the target speed and the actual speed. For gears available for a downshift, a gear-dependent maximum acceleration is determined. A limiting gear is determined depending on a comparison between the target acceleration and the gear-dependent maximum accelerations. If the target gear for a downshift determined depending on the or each shift characteristic map is lower than the limiting gear, a downshift is limited to the limiting gear. If the target gear for a downshift determined depending on the or each shift characteristic map is higher than or equal to the limiting gear, a downshift to the target gear determined depending on the or each shift characteristic map is permitted.

[0012] The present invention makes it possible to limit the number of downshifts requested and executed when reducing a difference between the target speed of the cruise control function and the actual speed of the motor vehicle. For this purpose, a limiting gear is determined based on the comparison between the target acceleration of the motor vehicle and gear-dependent or gear-specific maximum accelerations. The limiting gear can therefore ultimately also prevent excessive acceleration of the motor vehicle, which is perceived as uncomfortable.

[0013] According to an advantageous development, the target acceleration for the motor vehicle is additionally determined depending on the incline or decline on which the motor vehicle is operated, and / or depending on an active driving mode, and / or depending on the road surface, and / or depending on weather conditions, and / or depending on navigation data. This allows for a particularly advantageous determination of the target acceleration for the motor vehicle.

[0014] According to an advantageous further development, the gear-dependent maximum acceleration is determined as a function of a gear-dependent maximum possible force, as a function of driving resistance, and as a function of the mass of the motor vehicle. The gear-dependent maximum possible force is determined in such a way that a drive unit speed is determined for the respective gear as a function of the actual speed of the motor vehicle, a maximum possible drive unit torque is determined as a function of the drive unit speed and a full-load characteristic curve, and the gear-dependent maximum possible force is determined as a function of the maximum possible drive unit torque. This enables a particularly advantageous determination of the gear-dependent or gear-specific maximum acceleration.

[0015] According to an advantageous development, to determine the limiting gear, the gear-dependent maximum acceleration of a current gear is compared with the target acceleration. If the maximum acceleration of the current gear is less than the target acceleration, the current gear is preferably reduced by one gear and the gear-dependent maximum acceleration is again compared with the target acceleration. This is repeated until the maximum acceleration of the gear is greater than or equal to the target acceleration, in which case this gear is used as the limiting gear. This enables a particularly advantageous determination of the limiting gear.

[0016] The control device is defined in claim 10.

[0017] Preferred developments emerge from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail, without being limited thereto, with reference to the drawings. Herein: Fig. 1 an exemplary drive train diagram of a drive train of a motor vehicle; Fig. 2 a signal flow diagram to illustrate the invention; and Fig. 3 shows a further signal flow diagram to illustrate the invention.

[0018] The invention relates to a method and a control device for operating an automatic transmission of a motor vehicle with a cruise control function.

[0019] Fig. Figure 1 shows a highly schematic block diagram of a motor vehicle with a drive unit 1 and an automatic transmission 3 connected between the drive unit 1 and an output 2. Gears can be engaged automatically in the automatic transmission 3. Depending on the gear engaged in the automatic transmission 3, the transmission converts speeds and torques, thus providing the tractive power of the drive unit 1 to the output 2.

[0020] The operation of the drive unit 1 is controlled and / or regulated by an engine control unit 4, and the operation of the automatic transmission 3 is controlled and / or regulated by a transmission control unit 5. For this purpose, the engine control unit 4 exchanges data with the drive unit 1, and the transmission control unit 5 exchanges data with the automatic transmission 3. Furthermore, the engine control unit 4 and the transmission control unit 5 exchange data with each other.

[0021] When a cruise control function of the vehicle is active, it attempts to regulate the actual speed of the vehicle to a predefined target speed. However, it is possible, for example, for the driver to exit the cruise control function, in which case the actual speed may decrease, for example, when the vehicle is rolling or coasting. If the driver subsequently re-enters the cruise control function and returns to the previously applicable target speed, the difference between the actual speed and the target speed must be reduced.

[0022] A similar situation can occur with an adaptive cruise control function, especially if the distance to a preceding object decreases while the cruise control function is active. In this case, the adaptive cruise control function automatically reduces the actual speed of the vehicle below the target speed. If the distance to the preceding object subsequently increases again or the preceding object disappears, the actual speed should then be increased to the target speed.

[0023] The present invention now relates to such details by means of which, when the cruise control function is active and the actual speed of the motor vehicle is lower than the target speed of the motor vehicle and the difference between the target speed and the actual speed is to be reduced, the reduction can be carried out comfortably, in particular without excessive acceleration.

[0024] When the cruise control function is active and the difference between the target speed and the actual speed is to be reduced, power is requested from the motor vehicle's drive unit 1. Furthermore, depending on at least one shift map, which is typically stored in the transmission control unit 5, at least one downshift in the automatic transmission 3 is initially requested, followed, if necessary, by at least one upshift in the automatic transmission 3.

[0025] According to the invention, a target acceleration for the motor vehicle is determined depending on the actual speed and the difference between the target speed and the actual speed. Furthermore, a gear-dependent maximum acceleration is determined for gears available for a downshift. Depending on a comparison between the target acceleration and the gear-dependent maximum accelerations, a limiting gear for the automatic transmission 3 is determined. If the target gear for a downshift determined depending on the or each shift characteristic map is lower than the limiting gear, the downshift is limited to the limiting gear. However, if the target gear for a downshift determined depending on the or each shift characteristic map is higher than or corresponds to the limiting gear, the downshift is permitted and executed.The limiting gear therefore limits the number of downshifts. Excessive acceleration when reducing the difference between the target speed and the actual speed can be avoided, thereby increasing driving comfort and safety.

[0026] Further details of the invention are explained below with reference to the signal flow diagrams of Fig. 2 and Fig. 3 described.

[0027] Blocks 6 and 7 of the signal flow diagram of the Fig. 2 illustrates exemplary shift maps stored in the transmission control unit 5. Block 6 visualizes gradient-based, comfort-oriented shift maps, and block 7 visualizes gradient-based, performance-oriented shift maps.

[0028] In a block 8, depending on the switching maps of the Fig. 6 and Fig. Block 7 determines which shift(s) must be performed in automatic transmission 3 to reduce the difference between the target speed and the actual speed. Block 8 can then determine at least one downshift and, if necessary, at least one upshift.

[0029] Depending on the difference between the target speed of a cruise control function and the actual speed of the vehicle, either one of the switching maps of blocks 6 and 7 can be selected, or by interpolation between switching maps of the Fig. 6 and Fig. 7 an interpolated shift map is determined, on the basis of which at least one downshift and, if applicable, at least one upshift is determined in block 8.

[0030] The actual speed of the vehicle and the load requirement on the drive unit 1 are provided as input variables to a shift map, wherein the shift map then determines shifts on the control side depending on the actual speed of the motor vehicle and the load requirement on the drive unit 1, for example at least one downshift and subsequently, if necessary, at least one upshift.

[0031] Block 9 of the signal flow diagram of the Fig. 2 visualizes a check as to whether the target speed of the motor vehicle is greater than the actual speed of the motor vehicle when the cruise control function is active and whether a difference between the target speed and the actual speed should be reduced.

[0032] If this is the case, the system branches from block 9 to block 10, where the aforementioned limiting step is determined. Otherwise, the system branches to block 11, and no limiting step is determined.

[0033] The determination of the limiting gear in block 10 is based on a comparison between the determined target acceleration of the motor vehicle and the determined gear-dependent or gear-specific maximum accelerations of the gears available for a downshift of the automatic transmission 3. Block 10 of the Fig. 2 includes blocks 12 to 15 of the Fig. 3.

[0034] In block 12, a gear-dependent or gear-specific drive unit speed is first determined depending on the actual speed of the motor vehicle for the respective gear of the automatic transmission 1 available for a downshift.

[0035] In block 13, a gear-dependent or gear-specific maximum possible drive unit torque of the drive unit 1 is then determined depending on the gear-specific or gear-dependent drive unit speed, which is determined depending on the determined gear-specific drive unit speed and depending on a full-load characteristic curve for the respective gear.

[0036] Preferably, the full-load characteristic curve is dependent on the prevailing air pressure and / or intake air temperature. The gear-dependent or gear-specific maximum possible drive unit torque is therefore preferably determined based on the air pressure and the intake air temperature.

[0037] This maximum possible drive unit torque is determined in block 13 and provided to block 14, wherein in block 14 a gear-dependent, maximum possible force at the wheels of the output 2 of the motor vehicle is determined depending on the gear-specific or gear-dependent, maximum possible drive unit torque.

[0038] The gear-dependent or gear-specific, maximum possible force at the wheels of the output 2 is determined depending on a gear ratio of the automatic transmission 3 and / or depending on an efficiency of the automatic transmission 3 and / or depending on an axle ratio of the motor vehicle and / or depending on a diameter of the wheels of the output 2. The gear-dependent or gear-specific, maximum possible force is preferably determined at least depending on the gear ratio and the axle ratio. Preferably, the efficiency of the transmission and / or the diameter of the wheels of the output 2 are also taken into account.

[0039] This gear-dependent or gear-specific maximum possible force determined in block 14 is then provided to block 15, wherein in block 15 the respective gear-dependent or gear-specific maximum acceleration is determined depending on the dependent or gear-specific maximum possible force.

[0040] The respective gear-specific maximum acceleration depends on the respective maximum possible force, a driving resistance and a mass of the motor vehicle, whereby the difference between the gear-dependent, maximum possible force and the driving resistance is related to the vehicle mass in order to determine the gear-specific maximum acceleration.

[0041] The driving resistance consists of a speed-dependent component and a gradient-dependent component. The vehicle's mass is known by the control system.

[0042] In block 10, not only the gear-dependent or gear-specific maximum accelerations for the gears available for downshifting are determined, but also the target acceleration for the vehicle.

[0043] The target acceleration for the motor vehicle, which is gear-independent, is determined depending on the current actual speed of the motor vehicle, depending on the difference between the target speed and the actual speed, preferably depending on an incline and preferably depending on a driving mode selected by the driver.

[0044] The target acceleration for the motor vehicle is preferably additionally determined depending on the condition of the road surface and / or depending on weather conditions and / or depending on navigation data.

[0045] As already explained, the limiting gear is determined in block 10, depending on a comparison between the target acceleration and the gear-dependent or very specific maximum accelerations.

[0046] Starting with the current gear, its respective maximum acceleration is compared with the target acceleration. If the current gear offers a lower maximum acceleration than required by the target acceleration, the gear is preferably reduced by one gear. If the next lower gear also offers a lower maximum acceleration than required, the gear is preferably reduced again, preferably by one gear. This process is repeated until a gear is found whose maximum acceleration is greater than the target acceleration. This gear is then used as the limiting gear.

[0047] The limitation gear determined in block 10 and the gear determined in block 8 depending on at least one shift map are sent to block 16 of the Fig. 2, wherein in block 16 it is checked whether the gear determined in block 8 depending on at least one shift map is smaller than the limitation gear.

[0048] If this is the case, i.e. if the gear determined in block 8 depending on at least one shift map is lower than the limiting gear of block 10, then the system branches from block 16 to block 17, with downshifts then being limited to the limiting gear in block 17.

[0049] If, however, the gear determined as a function of the or each shift characteristic in block 8 is greater than or corresponds to the limiting gear of block 10, the system branches from block 16 to block 18, with downshifts in block 18 then not being limited to the limiting gear.

[0050] As already explained, the target acceleration is determined in block 10 based on the actual speed of the vehicle and the difference between the target speed and the actual speed. Furthermore, the target acceleration is preferably determined based on the vehicle's incline or decline and / or the driving mode selected by the driver.

[0051] Furthermore, when determining the target acceleration, road surface conditions, road type, weather conditions, time of day and / or season, navigation data or GPS data and the like can be taken into account.

[0052] The limitation of downshifts to the limiting gear in block 17 remains active until a gear is requested based on the or each shift characteristic in block 8 that is higher than or equal to the limiting gear. In this case, the limitation to the limiting gear is lifted, and gear changes are enabled without taking the limiting gear into account.

[0053] The invention is used when, with the cruise control function active, the actual speed of the motor vehicle is lower than the target speed and the difference between the target speed and the actual speed is to be reduced.

[0054] This can be the case with a cruise control or a non-adaptive cruise control function if the cruise control was first deactivated manually, the vehicle has slowed down and then the cruise control is subsequently reactivated manually at the old target speed by operating a resume or resumption element such as a button or switch.

[0055] Furthermore, this can be the case with the adaptive cruise control function if, when the cruise control function is active, the distance to an object in front decreases, so the actual speed of the motor vehicle is adjusted below the target speed and subsequently the distance to the object in front increases again and the actual speed is to be increased to the target speed.

[0056] Furthermore, this can be the case with a non-adaptive cruise control function and with an adaptive cruise control function when the target speed is increased.

[0057] Furthermore, this can be the case with a non-adaptive cruise control function and with an adaptive cruise control function if, for example, a speed limit and thus the target speed is increased, especially when leaving a built-up area.

[0058] The invention further relates to a control unit for operating the automatic transmission 3. The control unit according to the invention is preferably the transmission control unit 5. If, with the cruise control function active, an actual speed of the motor vehicle is less than a target speed of the motor vehicle, the control unit requests load from the drive unit 1 of the motor vehicle in order to reduce a difference between the target speed and the actual speed and, depending on at least one shift map, initially at least one downshift and then, if necessary, at least one upshift from the automatic transmission 3.

[0059] The control unit determines the target acceleration for the vehicle based on the actual speed and the difference between the target speed and the actual speed. The target acceleration, determined based on the actual speed and the difference between the target speed and the actual speed, can also be provided and read by another control unit, such as an engine control unit.

[0060] The control unit determines a gear-dependent maximum acceleration for gears available for downshifting. The control unit determines a limiting gear based on a comparison between the target acceleration and the gear-dependent maximum accelerations. If the target gear for a downshift, determined based on the or each shift map, is lower than the limiting gear, the control unit limits downshifting to the limiting gear.

[0061] If the target gear of a downshift determined as a function of the or each shift map is greater than or equal to the limiting gear, the control unit allows a downshift to the target gear determined as a function of the or each shift map.

[0062] The control unit according to the invention is preferably the transmission control unit 5. It has hardware and software for implementing the method. The hardware includes data interfaces for exchanging data with the relevant components of the motor vehicle, a processor for data processing, and a memory for data storage. The software includes program modules for implementing the method. Reference symbol 1 drive unit 2 downforce 3 automatic transmissions 4 Engine control unit 5 Transmission control unit 6 blocks 7 Blocks 8 blocks 9 Blocks 10 Block 11 Block 12 Block 13 Block 14 Block 15 Block 16 Block 17 Block 18 Block

Claims

[1] Method for operating an automatic transmission (3) of a motor vehicle, wherein, when an actual speed of the motor vehicle is lower than a target speed of the motor vehicle when the cruise control function is active, load is requested from a drive unit (1) of the motor vehicle in order to reduce a difference between the target speed and the actual speed, and depending on at least one shift map, at least one downshift and then, if necessary, at least one upshift is requested from the automatic transmission (3), characterized by , that a target acceleration for the motor vehicle is determined depending on the actual speed and depending on the difference between the target speed and the actual speed, for gears available for downshifting, a gear-dependent maximum acceleration is determined, a limiting gear is determined depending on a comparison between the target acceleration and the gear-dependent maximum accelerations, if the target gear of a downshift determined as a function of the or each shift map is lower than the limiting gear, a downshift is limited to the limiting gear, whereas if the target gear of a downshift determined as a function of the or each shift map is higher than or corresponds to the limiting gear, a downshift to the target gear determined as a function of the or each shift map is permitted. [2] Method according to claim 1, characterized by that the target acceleration for the motor vehicle is additionally determined depending on an uphill or downhill gradient on which the motor vehicle is operated and / or depending on an active driving mode. [3] Method according to claim 1 or 2, characterized bythat the target acceleration for the motor vehicle is additionally determined depending on the condition of the road surface and / or depending on weather conditions and / or depending on navigation data. [4] Method according to one of claims 1 to 3, characterized by that the respective gear-dependent maximum acceleration is determined depending on a gear-dependent maximum possible force, depending on a driving resistance and depending on a mass of the motor vehicle. [5] Method according to claim 4, characterized by that the gear-dependent, maximum possible force is determined in such a way that a drive unit speed is determined for each gear depending on the actual speed of the vehicle, a maximum possible drive unit torque is determined depending on the drive unit speed and a full load characteristic curve, Depending on the maximum possible drive unit torque, the gear-dependent, maximum possible force is determined. [6] Method according to claim 5, characterized by that the gear-dependent, maximum possible force is further determined depending on a gear ratio of the automatic transmission (3) and / or depending on an axle ratio and / or depending on a wheel diameter and / or depending on an efficiency of the automatic transmission (3). [7] Method according to claim 5 or 6, characterized by that the full load characteristic curve depends on a prevailing air pressure and / or a prevailing intake air temperature. [8] Method according to one of claims 1 to 7, characterized bythat to determine the limiting gear, starting from a current gear, the gear-dependent maximum acceleration of the same is compared with the target acceleration and then, if the maximum acceleration of the current gear is less than the target acceleration, the current gear is preferably reduced by one gear and the gear-dependent maximum acceleration of the same is again compared with the target acceleration, this being repeated until the maximum acceleration of the gear is greater than or equal to the target acceleration, this gear then being used as the limiting gear. [9] Method according to one of claims 1 to 8, characterized by that after the limitation of downshifts to the limiting gear has been achieved, the limitation remains active until a target gear determined depending on the or each shift map becomes higher than the limiting gear or corresponds to the same. [10] Control unit for operating an automatic transmission (3), wherein, when an actual speed of the motor vehicle is lower than a target speed of the motor vehicle when the cruise control function is active, the control unit requests load from a drive unit (1) of the motor vehicle to reduce a difference between the target speed and the actual speed and, depending on at least one shift map, initially requests at least one downshift and then, if necessary, at least one upshift from the automatic transmission (3), characterized by , that the control unit determines a target acceleration for the motor vehicle depending on the actual speed and the difference between the target speed and the actual speed, the control unit determines a gear-dependent maximum acceleration for gears available for downshifting, the control unit determines a limiting gear based on a comparison between the target acceleration and the gear-dependent maximum accelerations, the control unit limits a downshift to the limitation gear if the target gear of a downshift determined as a function of the or each shift characteristic map is lower than the limitation gear, whereas the control unit allows a downshift to the target gear determined as a function of the or each shift characteristic map if the target gear of a downshift determined as a function of the or each shift characteristic map is higher than or equal to the limitation gear. [11] Control device according to claim 10, characterized by that it carries out the method according to one of claims 1 to 9 on the control side.

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